Electron microscopy, for example SEM (scanning electron microscopy), is a powerful imaging modality that provides structural information at high spatial resolutions, typically a few nm (nanometers), due to the short DeBroglie wavelength of electrons at keV energies.
The interaction of keV electrons with a solid can produce CL (cathodoluminescent) photons, a phenomenon widely used for spatially-resolved characterization of semiconductors and insulators. For a variety of applications, including without limitation bio-imaging, it is desirable to supplement SEM structural data with functional information obtained by optical microscopy.
For imaging biological samples, the potential of CL to provide molecular localization has been recognized for some time. However, efforts to obtain nanoscale CL image resolution have been hindered by low photon count rates and rapid signal degradation due to the destruction of biomolecules and organic fluorophores under electron beam irradiation.